1. Field of the Invention
The invention relates to a process for the recovery from a reaction mixture of cellulose carbamate produced by conversion of cellulose with excess urea in an inert organic liquid reaction carrier.
2. Description of the Related Art
U.S. Pat. No. 5,378,827 discloses a multi-step process for the production of cellulose carbamate in which the cellulose is mixed with aqueous urea solution, the water portion of the mixture is exchanged for an organic reaction carrier, the conversion to the carbamate is carried out under formation or addition of an inert vaporous or gaseous medium which is led off from the reaction zone, a part of the organic reaction carrier is separated mechanically from the conversion mixture, the remaining mixture is added with aqueous urea solution, the remaining organic reaction carrier removed by distillation, the aqueous cellulose carbamate-containing mixture cooled by lowering its pressure, and the cellulose carbamate separated on a band filter from the aqueous urea solution and washed with water. The financial expense for the separation of the cellulose carbamate and the recovery of urea and reaction carrier is considerable.
According to DE-A 44 17 140, the organic reaction carrier can also be washed out with methanol or ethanol and recovered from the washing filtrate by extraction with water. The remaining extraction mixture can be separated by rectification in alcohol and aqueous urea solution. A disadvantage is that in addition to the reaction carrier, another auxiliary material must be used, namely, alcohol.
In the process of the EP Patent 97 685, the whole organic reaction carrier is separated from the reaction mixture through vacuum distillation and the remaining mixture washed with water. Because of the voluminous nature of the cellulose carbamate, there remains a considerable amount of organic reaction carrier in the cellulose carbamate after the distillation. Also, biuret, the by-product formed, is washed out only with difficulty.